At present, the water-reducing admixture commonly used in commercial can be divided into naphthalene based, melamine based and sulfamate based water-reducing admixture. With a great variation on the slumps, complex production process, high energy consumption and environmental pollution, the traditional naphthalene based, melamine based and sulfamate based water-reducing admixture cannot meet the needs of the era of low-carbon economy, the concrete industry and the sustainable development. With the increasingly high requirements in the durability and strength of concrete buildings during the engineering construction and application, a low mixing amount, high water-reducing rate, non-retarding, low slumping change, low energy consumption, safety and environmental friendly polycarboxylate superplasticizer is required.
The high performance polycarboxylate superplasticizer has many characteristics: (1) in the synthesis process, the high performance polycarboxylate superplasticizer is polymerized by unsaturated monomer rather than a polycondensation synthesis as traditional superplasticizer used. Thus, there are many raw materials for this type of water-reducing admixture. (2) in the molecular structure, the molecular structure of the polycarboxylate superplasticizer is a linear comb structure, rather than a single linear structure as the traditional water reducing agent. There are various active groups polymerized in the backbone of this kind of water-reducing admixture, such as the carboxy group (—COOH), hydroxyl group (—OH), sulfonic acid group (—SO3Na), etc., resulting in electrostatic repulsion effect. And the hydrophilic non-polar active groups in the side chain will result in a high steric hindrance effect. Because of its extensive source of raw materials, unique molecular structure, it has the advantages of unparalleled advantages compared to the previous two generations of water-reducing admixture. And because of formaldehyde free in the synthesis process, it is a green environmental production. Therefore, it has become a hot search and development focus in concrete research at home and abroad in recent years.
Chinese patent application CN103254418A reports a preparation method for a novel polycarboxylate superplasticizer using the polyether polyol as a raw material, comprising the following steps: (1) adding 3-30 parts of polyether polyol, 50-90 parts of mono-halogenated fatty acid or the salt thereof by weight, incubating in 65-75° C. for 1-3 hours; (2) adding 1-8 parts of catalyst by weight and raising the temperature to 80-120° C. for 2-4 hours; (3) cooling to 60-80° C., adding 10-40 parts of sulfonating agent by weight dropwise and incubating for 1-3 hours; (4) cooling to 20-60° C., adjusting the pH to 7.0-7.5 to obtain the target product. The water-reducing admixture obtain by this application has a good performance. And the preparation method thereof is simple and environmental friendly. However, the reaction temperature in step (1) of the above application is high, resulting in energy waste. Moreover, the utilizing ratio of the mother liquor of the polycarboxylate superplasticizer is relatively low and cannot be effectively utilized.